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Inner micrometer size 13

Inner micrometer size 13

Inner micrometer size 13

In a set of inner micrometer , why are they 2 odd size ?
size 13 and size 25

Why not 11 or 12 or 17 ?
Who invented it and why ?

RE: Inner micrometer size 13

You can stack these to achieve different total lengths, depending on what dimension you are measuring. The variation in size of the smallest device (the micrometer spindle) is about 1/2" or 13mm (ish?), so it measures a range from about 1.5 to 2", or 37 to 50mm. Add the smallest (13mm) extension, and you can measure about 50 to 63 mm, replace the 13mm with the 25mm, you get 62 to 75 mm, put the 13 and the 25 together with the micrometer spindle and get 75-100mm range, etc. etc.

Who invented it? From google - https://www.higherprecision.com/learning-center/fa...
"A man named William Gascoigne invented the very first micrometer in the 1600s. "

A bigger question, is why do you keep asking stupid questions that are easily answered by a google search?

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